Medusa was laid down as ML1387 at R A Newman & Sons of Poole Dorset on 27 July 1943 and launched on 20 October 1943. Under the command of Lt Maurice Liddiard RNVR she was involved in convoy escort in the Western Approaches before joining the 149th HDML Flotilla at Portsmouth and taking part in Exercise Fabius 1, which was a practise assault carried out by the Americans at Slapton Sands in Devon. Medusa took part in D day, arriving off Omaha beach the night before and staying on station throughout as navigational marker for approach channel 4.

In October 1944 she transferred to the 185 Auxilliary Minesweeping Flotilla based in the Medway.

Early in 1945 she went across to The Hague and from there to Ijmuiden where she accepted the surrender of the occupying German forces. From Ijmuiden she navigated the North Sea Canal to Amsterdam, the first allied ship to do so.

Post war Medusa was redesignated Fast Despatch Boat 76 before being allocated to London Division RNVR as HMS Thames. Subsequently she was renamed Seaward Defence Launch (SDML) 3516 and in 1953 became a survey vessel and was named HMS Medusa.

Medusa is powered by two Gardner 8L3 diesels and a Gardner 1L2 auxilliary. She is armed with two 20mm Oerlikon (originally one Oerlikon and a 3 Pounder), Two Vickers K machineguns and eight depth charges.

In 1968 she was sold by the Navy thought to be fit only for scrap. Since then, in private ownership, she has been maintained in her original configuration. She is now under the care of the Medusa Trust and is operated by volunteers from the Medusa Support Group. She is on the "Core Collection" of the National Historic Ships Committee and is berthed in Southampton